The field of fiber optics for conveying of communication data, voice, and data pulse trains has expanded greatly in recent years. The use of fiber optics transmission techniques is now well accepted in the telephone and data transmission arts. Optical multiplexing to enable each fiber to carry a great multitude of data and voice channels is well understood.
However, several technologies require the passage of power or communication signals (voice or data streams) across an interface between a rotary reference frame and a non rotary or stationary reference frame. One such application is the instrumentation of rotary devices, such as the rotors of electrical generators, when it is desired to collect stress, vibration, temperature, pressure, and other data form the apparatus in operation. In such a case, the necessary sensors and transducers mounted on the rotor of the apparatus, many of which are electrical, may have their data converted to optical signals, and passed through an optical rotary joint during operation of the apparatus. Similarly, command signals for the test apparatus on the rotor may be passed across the joint to the electrical test instruments while the apparatus is in operation. The techniques of optical multiplexing allow a limited number of optical fibers to suffice in this usage.
A conventional fiber optic rotary joint is provided by Focal Technologies of Dartmouth, Nova Scotia, Canada, which allows up to 10 optical fibers to feed into and out of the joint. This rotary joint permits unlimited members of rotations between the stationary and rotary parts of the joint. However, as noted above, the sensors and control devices aboard the rotating reference frame may be electrical powered, in which case either an on board power source must be provided, or power must be fed to the rotary apparatus another way. To this end, frequently, a fluidic, or electrical slip ring device is used in conjunction with a conventional fiber optic rotary joint. In the former case, the fluidic slip ring may simply carry pressure signals to a non rotational interpretation, recording, or indicating device. In the latter case, the electrical slip ring is employed to feed electrical power onto the rotary device, there to power electrical sensors, as well as the electrical-to-optical converters and optical multiplexing devices.
However, there exists a desire to provide communication with a device associated with a relatively rotating reference frame, which device is entirely optically powered. That is, only optical signals are to cross the rotating-stationary interface to and from the device. Further, in connection with the definition of this need it appears that unlimited numbers of relative rotations of the rotary reference frame are not required. A limited number of rotations of the rotary frame in each direction of rotation will suffice.
More particularly, a need exists to provide communication from a stationary frame to a plurality of sensors arrayed along a length of elongate sensor-carrier cable reeled upon or unreeled from a storage drum. Because the sensor-carrier cable is of finite length, a sufficient number of rotations of the storage drum to completely reel and unreel the cable will suffice. This use may require from a few turns to a few hundred turns of the storage drum. However, an unlimited number of turns of the storage drum is not required. However, communication with the sensors on the cable must be continuous, without interruption while or alteration of the transmittal optical signal the storage drum turns or is stationary. Communication to be provided may be via optical fibers, or with the use of electrical conductors, or other communication media conduits.